U.S. patent application number 13/550511 was filed with the patent office on 2012-11-08 for method and apparatus for enabling multiple passive optical networks to share one or more sources.
This patent application is currently assigned to AT&T Corp.. Invention is credited to PATRICK PAUL IANNONE, HAN HYUB LEE, KENNETH CHARLES REICHMANN, XIANG ZHOU.
Application Number | 20120281984 13/550511 |
Document ID | / |
Family ID | 46465534 |
Filed Date | 2012-11-08 |
United States Patent
Application |
20120281984 |
Kind Code |
A1 |
IANNONE; PATRICK PAUL ; et
al. |
November 8, 2012 |
METHOD AND APPARATUS FOR ENABLING MULTIPLE PASSIVE OPTICAL NETWORKS
TO SHARE ONE OR MORE SOURCES
Abstract
A method and apparatus for implementing a hybrid SOA-Raman
amplifier in a central office in order to enable multiple passive
optical networks to share one or more enhancement service sources,
e.g., to share a source for a broadcast service are disclosed.
Inventors: |
IANNONE; PATRICK PAUL; (Red
Bank, NJ) ; LEE; HAN HYUB; (Daejeon, KR) ;
REICHMANN; KENNETH CHARLES; (Hamilton, NJ) ; ZHOU;
XIANG; (Holmdel, NJ) |
Assignee: |
AT&T Corp.
New York
NY
|
Family ID: |
46465534 |
Appl. No.: |
13/550511 |
Filed: |
July 16, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11564245 |
Nov 28, 2006 |
8224183 |
|
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13550511 |
|
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Current U.S.
Class: |
398/68 |
Current CPC
Class: |
H04J 14/0246 20130101;
H04J 14/025 20130101; H04J 14/0282 20130101; H04J 14/0234 20130101;
H04J 14/0226 20130101; H04B 10/2916 20130101; H04B 10/2914
20130101 |
Class at
Publication: |
398/68 |
International
Class: |
H04J 14/02 20060101
H04J014/02 |
Claims
1. An optical network, comprising: a plurality of enhancement
service sources, where each of the plurality of enhancement service
sources provides source information; a plurality of light sources,
coupled to the plurality of enhancement service sources, where each
of the light sources is for modulating the source information from
one of the plurality of enhancement service sources to form a
modulated optical signal; a wave division multiplexer combiner,
coupled to the plurality of light sources, for combining the
modulated optical signals received from the plurality of light
sources; at least two hybrid semiconductor optical amplifier-raman
amplifiers, wherein a first of the at least two hybrid
semiconductor optical amplifier-raman amplifiers amplifies the
modulated optical signals in a first wavelength band, wherein a
second of the at least two hybrid semiconductor optical
amplifier-raman amplifiers amplifies the modulated optical signals
in a second wavelength band, wherein the first wavelength band is
different from the second wavelength band, wherein the at least two
hybrid semiconductor optical amplifier-raman amplifiers are coupled
to the wave division multiplexer combiner, wherein each of the at
least two hybrid semiconductor optical amplifier-raman amplifiers
is a two-stage amplifier that comprises a semiconductor optical
amplifier stage and a raman amplifier stage; and an optical
splitter, coupled to the at least two hybrid semiconductor optical
amplifier-raman amplifiers, wherein the optical splitter comprises
a plurality of outputs.
2. The optical network of claim 1, wherein the plurality of
enhancement service sources, the plurality of light sources, the
wave division multiplexer combiner, the at least two hybrid
semiconductor optical amplifier-raman amplifiers and the optical
splitter are deployed as a shared transmitter.
3. The optical network of claim 1, further comprising: a plurality
of wave division multiplexer band multiplexers, where each of the
plurality of wave division multiplexer band multiplexers is coupled
to one of the plurality of outputs of the optical splitter.
4. The optical network of claim 3, further comprising: a plurality
of optical line termination devices, where each optical line
termination device having a transceiver for sending and receiving
optical signals; and wherein each of the plurality of wave division
multiplexer band multiplexers multiplexes a split signal from one
of the plurality of outputs of the optical splitter with an optical
signal from one of the plurality of optical line termination
devices.
5. The optical network of claim 1, wherein the optical splitter is
a passive optical splitter.
6. The optical network of claim 4, wherein the optical splitter has
a splitting ratio of 1:M, where M correlates with the plurality of
optical line termination devices.
7. The optical network of claim 4, wherein each of the plurality of
optical line termination devices is associated with a separate
passive optical network.
8. The optical network of claim 4, wherein each of the plurality of
optical line termination devices having a downstream transmission
band of 1470 nm-1530 nm.
9. The optical network of claim 1, wherein the source information
comprises at least one of: internet protocol packets transmitted as
a base-band signal, a digital video signal modulated on a radio
frequency carrier, and an analog video signal modulated on a radio
frequency carrier.
10. An optical network, comprising: a plurality of enhancement
service source means, where each of the plurality of enhancement
service source means provides source information; a plurality of
light source means, coupled to the plurality of enhancement service
source means, where each of the light source means is for
modulating the source information from one of the plurality of
enhancement service source means to form a modulated optical
signal; a wave division multiplexer combining means, coupled to the
plurality of light source means, for combining the modulated
optical signals received from the plurality of light source means;
at least two hybrid semiconductor optical amplifier-raman
amplifying means, wherein a first of the at least two hybrid
semiconductor optical amplifier-raman amplifying means amplifies
the modulated optical signals in a first wavelength band, wherein a
second of the at least two hybrid semiconductor optical
amplifier-raman amplifying means amplifies the modulated optical
signals in a second wavelength band, wherein the first wavelength
band is different from the second wavelength band, wherein the at
least two hybrid semiconductor optical amplifier-raman amplifying
means are coupled to the wave division multiplexer combining means,
wherein each of the at least two hybrid semiconductor optical
amplifier-raman amplifying means is a two-stage amplifier means
that comprises a semiconductor optical amplifier stage and a raman
amplifier stage; and an optical splitting means, coupled to the at
least two hybrid semiconductor optical amplifier-raman amplifying
means, wherein the optical splitting means comprises a plurality of
outputs.
11. The optical network of claim 10, wherein the plurality of
enhancement service source means, the plurality of light source
means, the wave division multiplexer combining means, the at least
two hybrid semiconductor optical amplifier-raman amplifying means
and the optical splitting means are deployed as a shared
transmitter.
12. The optical network of claim 10, further comprising: a
plurality of wave division multiplexer band multiplexing means,
where each of the plurality of wave division multiplexer band
multiplexing means is coupled to one of the plurality of outputs of
the optical splitting means.
13. The optical network of claim 12, further comprising: a
plurality of optical line terminating means, where each optical
line termination means having a transceiver for sending and
receiving optical signals; and wherein each of the plurality of
wave division multiplexer band multiplexing means multiplexes a
split signal from one of the plurality of outputs of the optical
splitting means with an optical signal from one of the plurality of
optical line terminating means.
14. The optical network of claim 10, wherein the optical splitting
means is a passive optical splitter.
15. The optical network of claim 13, wherein the optical splitting
means has a splitting ratio of 1:M, where M correlates with the
plurality of optical line terminating means.
16. The optical network of claim 13, wherein each of the plurality
of optical line termination means is associated with a separate
passive optical network.
17. The optical network of claim 13, wherein each of the plurality
of optical line terminating means having a downstream transmission
band of 1470 nm-1530 nm.
18. The optical network of claim 10, wherein the enhancement
service source information comprises at least one of: internet
protocol packets transmitted as a base-band signal, a digital video
signal modulated on a radio frequency carrier, and an analog video
signal modulated on a radio frequency carrier.
19. A method for providing an optical network, comprising:
providing a plurality of enhancement service sources, where each of
the plurality of enhancement service sources provides source
information; providing a plurality of light sources, coupled to the
plurality of enhancement service sources, where each of the light
sources is for modulating the source information from one of the
plurality of enhancement service sources to form a modulated
optical signal; providing a wave division multiplexer combiner,
coupled to the plurality of light sources, for combining the
modulated optical signals received from the plurality of light
sources; providing at least two hybrid semiconductor optical
amplifier-raman amplifiers, wherein a first of the at least two
hybrid semiconductor optical amplifier-raman amplifiers amplifies
the modulated optical signals in a first wavelength band, wherein a
second of the at least two hybrid semiconductor optical
amplifier-raman amplifiers amplifies the modulated optical signals
in a second wavelength band, wherein the first wavelength band is
different from the second wavelength band, wherein the at least two
hybrid semiconductor optical amplifier-raman amplifiers are coupled
to the wave division multiplexer combiner, wherein each of the at
least two hybrid semiconductor optical amplifier-raman amplifiers
is a two-stage amplifier that comprises a semiconductor optical
amplifier stage and a raman amplifier stage; and providing an
optical splitter, coupled to the at least two hybrid semiconductor
optical amplifier-raman amplifiers, wherein the optical splitter
comprises a plurality of outputs.
20. The method of claim 19, further comprising: providing a
plurality of wave division multiplexer band multiplexers, where
each of the plurality of wave division multiplexer band
multiplexers is coupled to one of the plurality of outputs of the
optical splitter.
Description
[0001] This application is a continuation of U.S. Ser. No.
11/564,245, filed Nov. 28, 2006, which is currently allowed and is
hereby incorporated by reference in its entirety.
[0002] The present application is related to U.S. Ser. No.
11/564,237, filed Nov. 28, 2006, entitled "METHOD AND APPARATUS FOR
PROVIDING PASSIVE OPTICAL NETWORKS WITH EXTENDED REACH AND/OR
SPLIT", and U.S. patent application Ser. No. 11/564,239, filed Nov.
28, 2006, entitled "METHOD AND APPARATUS FOR ENABLING MULTIPLE
OPTICAL LINE TERMINATION DEVICES TO SHARE A FEEDER FIBER," where
both applications are herein incorporated by reference in their
entirety.
[0003] The present invention relates generally to communication
networks and, more particularly, to a method and apparatus for
enabling multiple passive optical networks to share one or more
enhancement service sources.
BACKGROUND OF THE INVENTION
[0004] A passive optical network typically comprises an Optical
Line Termination (OLT) located at a service provider site, a
splitter located between the service provider site and the
plurality of customer sites, and a plurality of Optical Network
Terminations (ONT), e.g., 32 ONTs, for serving the customers. The
passive optical network has limitations due to signal level
requirements of the transceiver components in the OLT and ONTs. For
example, a typical passive optical network may limit the distance
between the OLT and the farthest ONT to be 20 km with an 1:32 split
ratio due to the attenuation of the optical signals. However, as
service providers expand their network, serving more and more
customers with the same network and being able to extend the reach
of the passive optical network become more and more important.
Providing a passive optical network for every 32 customers does not
allow service providers to reduce the cost of the network, i.e.,
there is minimal sharing of network resources. For example, an
enhancement service source such as a video broadcast feed may have
to be duplicated for every 32 customers.
[0005] Therefore, there is a need for a method and apparatus that
enables multiple passive optical networks to share one or more
sources for enhancement services.
SUMMARY OF THE INVENTION
[0006] In one embodiment, the present invention discloses a method
and apparatus for implementing a hybrid SOA-Raman amplifier in a
central office in order to enable multiple passive optical networks
to share one or more sources for enhancement services, e.g., to
share a source for a broadcast service. For example, the optical
network comprises a plurality of enhancement service sources, where
each of the plurality of enhancement service sources provides
source information. The optical network further comprises a
plurality of light sources, coupled to the plurality of enhancement
service sources, where each of the light sources is for modulating
the source information from one of the plurality of enhancement
service sources to form a modulated optical signal. The optical
network further comprises a wave division multiplexer (WDM)
combiner, coupled to the plurality of light sources, for combining
the modulated optical signals received from the plurality of light
sources. The optical network further comprises at least one hybrid
SOA-Raman amplifier, wherein the at least one hybrid SOA-Raman
amplifier is coupled to the WDM combiner. Finally, the optical
network further comprises at least one optical splitter, coupled to
the at least one hybrid SOA-Raman amplifier, wherein the at least
one optical splitter comprises a plurality of outputs.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The teaching of the present invention can be readily
understood by considering the following detailed description in
conjunction with the accompanying drawings, in which:
[0008] FIG. 1 illustrates an exemplary network of the current
invention;
[0009] FIG. 2 illustrates an exemplary embodiment of a PON of the
current invention;
[0010] FIG. 3 illustrates the optical extender box of the current
invention;
[0011] FIG. 4 illustrates an exemplary embodiment with four PONs
sharing a common feeder;
[0012] FIG. 5 illustrates an exemplary embodiment for multiplying
the number of ONTs served by a feeder fiber; and
[0013] FIG. 6 provides an exemplary network with PONs heavily
sharing sources.
[0014] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures.
DETAILED DESCRIPTION
[0015] The present invention broadly discloses a method and
apparatus for providing passive optical networks with extended
reach and/or splitting ratio. Although the present invention is
discussed below in the context of passive optical networks, the
present invention is not so limited. Namely, the present invention
can be applied to extend the reach of other fiber optic networks
such as long haul and access networks.
[0016] The current invention discloses various passive optical
networks that are based on the hybrid SOA-Raman amplifier. In one
embodiment, the reach and/or splitting ratio of passive optical
networks can be extended using a hybrid SOA-Raman amplifier. In
another embodiment, multiple passive optical networks may share a
feeder fiber by using the optical gain of a hybrid SOA-Raman
amplifier. In yet another embodiment, multiple passive optical
networks are enabled to share source signals for enhancement
services via a hybrid SOA-Raman amplifier deployed at a central
office.
[0017] FIG. 1 illustrates an exemplary network 100 of the current
invention. Customer endpoint devices 102-104 are connected to the
service provider's network 110 through a passive optical network
101 to receive voice and data services. The Passive Optical Network
(PON) is used to deliver optical fiber signals to the end user,
e.g. fiber-to-the-home systems, fiber-to-the-curb systems, etc.
[0018] FIG. 2 illustrates an exemplary embodiment of a PON 200 of
the current invention. In describing the interactions of the
different components in FIG. 2, those skilled in the art would
realize that FIG. 2 may also serve as a flowchart for describing
the methodology for increasing the distance between the OLT and the
ONTs and/or increasing the splitting ratio such that more ONTs may
be serviced by the same splitter.
[0019] PON 200 may comprise an Optical Line Termination (OLT)
device 240 located at a service provider's site 260 (e.g., at a
central office), an optical extender box 280 of the current
invention, a passive optical splitter 245 located at a remote node
250 (e.g., located close to the customer end devices), and a number
of Optical Network Termination (ONT) devices 201.sub.1-201.sub.64.
In one embodiment, the central office 260 is part of the service
provider's network. Depending on the location of the optical fiber
termination, the ONTs 201.sub.1-201.sub.64 may be located at the
customer site, at the curb, and so on. The location of the ONTs
determines whether the system is described as fiber-to-the-curb
(FTTC), fiber-to-the-building (FTTB), fiber-to-the-home (FTTH),
fiber-to-the-node (FTTN), or in the most general terms, FTTx.
[0020] A transceiver located on the OLT 240 is connected to the
passive optical splitter 245 via a feeder fiber (e.g., standard
single mode fiber) 265 and optical extender 280. The optical
extender box 280 may be located in a remote node at an optimal
distance for amplifying the optical signals received from the OLT
240. The passive optical splitter 245 is connected to the ONTs
201.sub.1-201.sub.64 via distribution fibers 270. The term
"passive" refers to the fact that the device has no power
requirements or active electronic parts. In one embodiment,
identical optical signals are distributed to all the ONTs. Note
that the power of the optical signal received by an ONT is a small
fraction of the optical power received by the splitter. In one
embodiment, a de-multiplexer is used within each ONT to limit the
received optical bandwidth (or wavelength) to the desired signal
for each user. Due to the power margins of laser transmitters and
photo detectors used in the OLT and ONT transceivers, the maximum
reach for a PON without the optical extender 280 of the current
invention is often limited. For example, for a PON with a splitting
ratio of 1:32 and an optical signal transmission over single mode
optical fibers, the distance between the OLT and the farthest ONT
is often limited to 20 km. However, the optical extender box 280 of
the current invention may amplify the optical signals such that the
distance between the OLT and the farthest ONT may be increased to
60 km (e.g., 40 km for a first standard single mode fiber section
and 20 km for a second standard single mode fiber section deployed
on either side of the optical extender box) and the splitting ratio
may be increased, e.g., to 1:64.
[0021] In one embodiment, the wavelength plan for TDM traffic on
passive optical networks is downstream transmission in the band of
1480-1500 nm wavelengths, and upstream transmission in the band of
1260-1360 nm wavelengths. However, as businesses and services
expand delivering "multiple" services on fiber links as close as
possible to the customers becomes more and more important.
[0022] In one embodiment, the current invention enables the service
provider to optionally provide additional services using other
wavelengths. Thus, the optical extender box 280 of the current
invention may amplify not only the regular TDM signal but also as
many as three or four additional Coarse Wavelength Division
Multiplexing (CWDM) wavelengths. The additional wavelengths may be
used to provide video and data services. For example, depending on
economic and technical considerations, the CWDM wavelengths
centered at 1510 nm, 1530 nm, and 1550 nm may be used each with a
distinct downstream service, or a larger number of a Dense Wave
Division Multiplexing (DWDM) wavelengths may be used. Each
enhancement wavelength may carry a separate downstream service.
[0023] In one embodiment, the WDM combiner 281 located at the
central office 260 is used to combine the CWDM signals sourced by a
plurality of enhancement OLTs, e.g., video OLT 276, other
enhancement service OLTs 277 and 278, with the TDM signals coming
from the PON OLT 240. The combined optical signal is then
transmitted on feeder fiber 265 towards the optical extender box
280. For customers who subscribe to the enhanced data and video
services, their ONT 201.sub.64 includes a WDM splitter 282
(de-multiplexer) that directs the enhancement wavelengths and the
standard PON wavelength signals to one or more distinct optical
receivers for detecting the specific services. For example, if a
customer subscribed to a video service provided on a particular
CWDM wavelength, the optional ONT 201.sub.64 for said customer
includes a de-multiplexer that separates the CWDM wavelength from
the signal to be directed to the regular TDM receiver. The WDM
splitter 282 directs the enhancement wavelength (the CWDM
wavelength being used for video) to a distinct optical receiver
that detects the video service.
[0024] FIG. 3 illustrates the optical extender box 280 of the
current invention. The wavelength diplexers 301 and 302 are used to
separate and recombine the downstream and upstream wavelengths. The
wavelength plan for Time Division Multiplexed (TDM) traffic on
passive optical networks is downstream transmission (e.g., towards
customer) in the band of 1480-1500 nm wavelengths, and upstream
transmission (e.g., towards service provider) in the band of
1260-1360 nm wavelengths. The lower leg or portion 310 contains a
hybrid SOA-Raman amplifier for the downstream signals and the upper
leg or portion 320 contains a hybrid SOA-Raman amplifier for the
upstream signals.
[0025] The hybrid SOA-Raman amplifier is a two-stage amplifier
comprising a conventional semiconductor optical amplifier (SOA)
followed (or preceded depending on the implementation) by a
low-powered Raman amplifier stage. The combination of SOA gain and
Raman gain results in an amplifier with high and flat gain. For
each leg, the high gain is determined by the peak gain of the SOA
stage. Note that the gain of the SOA stage decreases monotonically
with increasing wavelength. The flatness of the gain is due to the
gain of the Raman amplifier stage that comprises a Raman pump
laser, a pump coupler, and a non-linear fiber. The gain of the
Raman amplifier stage acts to compensate for the monotonic decrease
in the gain of the SOA stage. The optical bandwidth of the hybrid
SOA-Raman amplifier may exceed 100 nm with a gain flatness of
approximately 1 dB or better. Since the amplifier has a total
bandwidth exceeding 100 nm, it is capable of amplifying the 1490
band (from 1480 to 1500 nm) and enhancement wavelengths in the
range 1500 to 1580 nm. The loss of any additional transmission
fiber is assumed to be 0.4 dB/km and the loss associated with each
doubling of the splitting ratio is slightly more than 3 dB.
[0026] For example, in a system with 10 km of added fiber and a
splitting ratio that has been increased by a factor of 4 to 1:128
(doubled twice), the amplifier needs to have a gain of at least 10
dB (4 dB to overcome the fiber loss and 2.times.3 dB to overcome
the additional splitting loss). Similarly, for a system with 40 km
of additional fiber and 1:64 split, the gain of the hybrid
amplifier needs to be at least 19 dB. A downstream gain of 20 dB is
therefore large enough to compensate the maximum loss of 16 dB
associated with an additional 40 km of fiber plus an additional
3-dB of splitting loss for increasing the split ratio from 1:32 to
1:64 (1 dB spare). Also, since the Raman gain is only used to
compensate the non-flat response of the SOA, only moderate Raman
pump powers are required, resulting in a more practical, higher
gain, and a more cost effective design than an all-Raman amplifier.
Furthermore, since both SOAs and Raman amplifiers can be designed
for any band within the low-loss window of optical fibers, hybrid
SOA-Raman amplifiers may be designed to meet any wavelength
specifications. As such, enhancement wavelengths can be deployed by
a service provider. For example, the three enhancement wavelengths
(as discussed below) are chosen to coincide with standard CWDM
channels at 1510, 1530, and 1550 nm.
[0027] Although FIG. 3 illustrates an optical extender 280 having
two hybrid SOA-Raman amplifiers 310 and 320, there may be scenarios
where only a single hybrid SOA-Raman amplifier is required. For
example, in one embodiment, the upstream wavelength (at 1310 nm) is
amplified using a conventional SOA stage, e.g., amplifier 320 is
replaced with a conventional SOA. For example, the upstream signal
may not require the hybrid SOA-Raman amplifier. There may be a
small power penalty (-1 dB) due to chromatic dispersion associated
with the increased transmission distance and added optical noise
from the amplifier subsystem at this wavelength. For example, in
one embodiment, an optical filter centered on the 1310-nm upstream
channel may be included between the upstream SOA and the OLT
receiver to limit the spontaneous noise added by the SOA. Note
that, the downstream signals do not require additional optical
filtering since the demultiplexer within each ONT limits the
optical bandwidth (and hence the noise bandwidth) of each
channel.
[0028] For the optical extender box 280 illustrated in detail in
FIG. 3, the isolators 322 and 312 are used to limit optical signals
in the opposite direction to the transmission. For example, for the
downstream signals on leg or portion 310, the pump laser 315 may
insert optical signal at 1440 nm. The pump coupler 314 then couples
the pump signal with the downstream signals. The downstream signals
are amplified as both signals propagate in the highly non-linear
fiber 313. The isolator 312 blocks the pump wavelength from
reaching the SOA 311. For the upstream leg or portion 320, the pump
laser 325 inserts optical signal at 1260 nm. The coupler 324
couples the pump signal with the upstream signal. The upstream
signal is amplified as both signals propagate through the highly
non-linear fiber 323. The isolator 322 prevents the pump signal
(1260 nm signal) from reaching the SOA 321.
[0029] In the above description, the pump wavelengths for the
downstream and upstream signals were 1440 nm and 1260 nm,
respectively. However, the wavelength for each pump laser may be
chosen at a different nearby wavelength to optimize performance.
For example, the upstream SOA 321 may be chosen to have a gain peak
near 1280 nm and the downstream SOA 311 may be chosen to have a
gain peak near 1460 nm. In addition, the SOA stage is shown as the
first stage in FIG. 3. However, those skilled in the art would
realize the order of the SOA and discrete Raman stages may be
reversed depending on their relative performance.
[0030] In one embodiment, the current invention enables two or more
PONs to share a common feeder fiber by sharing an extender box. By
choosing distinct pairs of CWDM wavelengths for each PON, multiple
PONs may share a common feeder fiber. Unique pairs of standard CWDM
wavelengths are used to establish downstream and upstream
communication for several PONs over a common infrastructure.
[0031] In one embodiment, the bandwidth available for each ONT is
increased by subdividing a PON and using an extender box. FIG. 4
illustrates an exemplary embodiment 400 with four PONs sharing a
common feeder. In describing the interactions of the different
components in FIG. 4, those skilled in the art would realize that
FIG. 4 may also serve as a flowchart for describing the methodology
for increasing the bandwidth available for each ONT by allowing
multiple ONTs to share a feeder fiber.
[0032] For example, WDM 481 located at the central office 460 may
connect a plurality of PON OLTs, e.g., the 4 PON OLTs 440-443 to
the feeder fiber 465. The combined signal is transmitted towards
the splitter 445 through the optical extender box 480. The ONTs
401-432 may have wavelength filters in order to pass only the
wavelength intended for that ONT. Members of a given sub-PON (e.g.,
a subgroup of ONTs 401-408, ONTs 409-416, ONTs 417-424, or ONTs
425-432) would use the same optical filter to receive down stream
information from a specific PON OLT (e.g. 440, 441,442 or 443) and
also would transmit on the same upstream CWDM wavelength.
[0033] In another embodiment, the number of ONTs served by each
feeder fiber is increased by using an extender box. FIG. 5
illustrates an exemplary embodiment 500 for multiplying the number
of ONTs served by a feeder fiber. In describing the interactions of
the different components in FIG. 5, those skilled in the art would
realize that FIG. 5 may also serve as a flowchart for describing
the methodology for increasing the number of ONTs served by each
feeder fiber.
[0034] For example, a 1:P WDM 582 analogous to the one used at the
central office is provided at a remote node 545. The WDM 582
directs the wavelength (in both directions) for each of the P
passive optical networks to and from a distinct passive splitter
(591, 592, 593 or 594) connected to that PON's distribution fibers
serving N ONTs. Each of the passive splitters is shown serving 32
ONTs. Table 1 provides an exemplary wavelength plan for sharing the
feeder fiber among 4 PONs. The wavelengths are chosen on the CWDM
grid.
TABLE-US-00001 TABLE 1 An exemplary wavelength plan for PONs
sharing a common feeder fiber. PON 1 PON 2 PON 3 PON 4 Downstream
Wavelength 1 Wavelength Wavelength Wavelength wavelength 1470 nm 2
3 4 1490 nm 1510 nm 1530 nm Upstream Wavelength 5 Wavelength
Wavelength Wavelength wavelength 1290 nm 6 7 8 1310 nm 1330 nm 1350
nm
[0035] In one embodiment, the current invention enables two or more
PONs to share sources for downstream wavelength services by
implementing the extender box at the central office. For example,
sources for downstream services, e.g. a high definition TV source,
may be heavily shared among several PONs to reduce the per
subscriber cost. This embodiment permits more economical broadcast
service by enabling the cost of the hybrid SOA-Raman amplifier and
laser sources to be shared among many users (via multiple
PONs).
[0036] FIG. 6 provides an exemplary network 600 with PONs heavily
sharing sources. In describing the interactions of the different
components in FIG. 6, those skilled in the art would realize that
FIG. 6 may also serve as a flowchart for describing the methodology
for enabling more than one PON to share a source signal.
[0037] For example, each of the four un-cooled CWDM Distributed
Feedback (DFB) laser diodes 611-614 (broadly referred to as light
sources) is directly modulated with one of the broadcast service
sources 601-604 for providing source information. The broadcast
services 601-604 may comprise of IP packets transmitted as a
base-band signal (e.g. Internet protocol based TV (IPTV)), or may
comprise of digital video streams modulated onto radio frequency
(RF) carriers, or may comprise of analog video signals modulated
onto RF carriers, or some other electrical format. The modulated
optical signals from the four lasers 611-614 are combined in a WDM
multiplexer 620.
[0038] In one embodiment, a power combiner may be used instead of
the WDM multiplexer. The output of the multiplexer 620 is then
input into a hybrid SOA-Raman amplifier 630 such that the output
power is substantially higher than the output power of each of the
DFB laser transmitters 611-614. The output of the hybrid SOA-Raman
amplifier 630 is input into a passive 1:M splitter 640. Each of the
M outputs from the splitter 640 having a split signal is connected
to a WDM band multiplexer 650a-650m. The signal from the PON OLT
for each of the M passive optical networks (660a-660m) is
multiplexed with the corresponding signal from one of the M
distinct signals coming from the splitter 640 in the appropriate
multiplexer. The output of the multiplexer is then fed to a PON via
a respective 670a-670m feeder. For example, the signal from the PON
OLT 660a is multiplexed with the corresponding signal coming from
the splitter 640 in multiplexer 650a. The output of the multiplexer
650a is fed to a PON via feeder 670a. Each of the PONs being fed
via 670a-670m may each be PONs of the current invention illustrated
in FIG. 2.
[0039] Thus, for a hybrid amplifier with output power of +20 dBm
per channel, the splitting ratio following the amplifier might be
1:32 (typically corresponding to .ltoreq.17 dB splitting loss) and
the excess loss of the WDM band mux may be 1 dB or less, resulting
in +2 dBm launched into the feeder fiber (which is comparable to
the expected launch power per channel in a standard PON). For the
example as shown in FIG. 6, the components 601-604, 611-614, 620,
630 and 640 may comprise a shared transmitter 645 and may serve
32.times.32=1024 users. It has been observed that using the shared
transmitter 645 will significantly lower the cost per PON when
compared to conventional transmitters.
[0040] While various embodiments have been described above, it
should be understood that they have been presented by way of
example only, and not limitation. Thus, the breadth and scope of a
preferred embodiment should not be limited by any of the
above-described exemplary embodiments, but should be defined only
in accordance with the following claims and their equivalents.
* * * * *